Various prior art practitioners have sought to control oxygen in the as-grown silicon crystals. Typical of these are those now to be described.
U.S. Pat. No. 2,998,335 issued Aug. 29, 1961 to Dehmelt describes a method of moving the heater axially with respect to the crucible during crystal growth. Also during growth both the crystal and crucible are rotated and the crystal is moved axially with respect to the melt surface.
U.S. Pat. No. 3,359,077 issued Dec. 19, 1969 to Arst discloses a method wherein the crucible position is initially adjusted such that as the melt level in the crucible recedes, the level changes within the constant temperature region of the heater.
U.S. Pat. No. 3,929,557 issued Dec. 30, 1975 to Goodrum, teaches the alternate acceleration and deceleration of the crystal rotation rate to improve crystal quality.
U.S. Pat. No. 3,953,281 issued Apr. 27, 1976 to Pantusco et al. discloses a Czochralski crystal growing apparatus with separately controllable means for providing independent rotational and axial movement of the crystal and crucible. The teaching is to maintain the melt surface within the isothermal region of the heater.
The so-called crucible interrupt method of crystal growth is disclosed in U.S. Pat. No. 4,040,895 issued Aug. 9, 1977 to Patrick et al.
The Koehl U.S. Pat. No. 4,239,585 issued Dec. 16, 1980, teaches increasing the rotational speed of the crystal as the growth proceeds.
While each of the foregoing practitioners sought to control oxygen and/or improve crystal quality, none of them provided an interrelated control over the critical process parameters to achieve a uniform radial oxygen distribution, a uniform axial distribution, or a uniform oxygen distribution in both the radial and axial directions in the as-grown crystal.